The present invention relates to a method and apparatus for evaluating exposed and developed film frames or analogous portions of information which is stored on elongated web-like carriers, especially for evaluating frames of exposed and developed color films prior to reproduction of such frames as a copying station. More particularly, the invention relates to a method and apparatus for selecting, storing and transmitting appropriate data to the exposure controls of a copying machine wherein portions of information which is stored on a web-like carrier are reproduced on photographic copy paper or other copying material.
Automatic copying machines for color photographic negatives are often, and particularly invariably, equipped with automatic (objective) evaluating systems which generate signals whenever the color balance and/or density of a frame is such that the exposure controls must be adjusted if the copying machine is to make an acceptable reproduction. The objective evaluating system scans each frame of a succession of frames on a web of color film and produces signals whenever the color balance and/or density of a frame deviates from an average value. The signals reach the exposure controls of the copying machine simultaneously with advancement of the respective frames into register with the copying station. The objective evaluating system can be installed in the copying machine proper so that it examines or inspects that frame which is already located at the copying station. Alternatively, the objective evaluating system can be installed ahead of the copying station and is then operatively connected with the exposure controls so as to insure that the signals reach the exposure controls simultaneously with the arrival of corresponding frames at the copying station.
It is further known to design the objective evaluating system as a discrete apparatus through which an entire web or a series of webs of photographic film advance upstream or ahead of the copying machine. Such apparatus are known as prereaders, and they are often equipped with means for determination and recording of certain other characteristics of film frames, e.g., lack of sharpness, failure to expose on or more frames, and/or others. The signals which are furnished by the prereader are stored on a suitable data carrier, e.g., a perforated tape, a magnetic tape or a magnetic disk. The data carrier is then introduced into the copying machine and the data which are stored thereon are decoded and transmitted to the exposure controls in synchronism with the placing of corresponding film frames into register with the copying station. The provision of a separate prereader exhibits the advantage that the evaluation of frames on a web of photographic film need not be synchronized with the reproduction of images of film frames in the copying machine. The integration of a prereader into the copying machine also exhibits certain advantages, especially that the means for storing data which must be transmitted to the exposure controls is simpler and more compact because it normally suffices to store data pertaining to a relatively small number of successive film frames.
The copying of color photographic negatives is normally carried out as follows: The integral color densities are measured at the copying station in the customary way. The results of such measurements are transmitted to the exposure controls, together with data from the prereader (such data are normally indicative of necessary density or color corrections when the tonal distribution and/or density of the respective frames deviates from an average value). The exposure controls then determine the exposure times in the three basic colors (red, blue and green).
It has been found that automatic prereaders of presently known design cannot insure the making of satisfactory reproductions of each and every frame on a relatively long web of photographic film. The reasons for such unreliability of prereaders are manifold. For example, these components of a prereader which monitor the density of the film frames often transmit signals for adjustment of the exposure controls so as to carry out a density correction even though the density of the respective film frame is quite satisfactory. This is due to the fact that a density correction is warranted only if this results in improved reproduction of an essential or dominant portion or section of a film frame. Correction of density in one or more secondary or non-essential portions or sections of the reproduced film frame often affects the quality of the reproduction because the density of the critical section deviates from satisfactory density. The prereader cannot discriminate between critical or dominant and secondary portions of a film frame even if the frame is subdivided into two or more imaginary areas or fields one of which is assumed to be (or to be likely to be) the dominant field. Reference may be had to commonly owned U.S. Pat. No. 3,523,728 granted Aug. 11, 1970 to R. Wick et al. In accordance with the teaching of this patent, the density of the dominant field of the frame is monitored independently of the secondary field or fields. A fully automatic prereader cannot properly evaluate the film frames according to imaginary or theoretical division into several fields of different importance, mainly because the dominant field is not always located in the same position especially since certain frames are exposed with the camera held in upright position and other frames are exposed with the camera held in horizontal positon or another position of inclination with respect to vertical.
As regards the color correction components of an automatic prereader, they are likely to select excessive or insufficient color correction values. This will be readily appreciated by considering that an automatic prereader cannot discriminate between intentional dominant colors and an unintentional color shade. For example, a vacationer is likely to make a large number of exposures on the beach where the blue color of the sky is predominant. An automatic prereader will invariably produce signals for excessive color correction of corresponding reproductions, i.e., the reproductions will be quite unsatisfactory. The same applies for exposures with a predominance of green (pictures of meadows, forests, etc.), grey (pictures of rocky mountains) and/or other colors.